Field of the Disclosure
Embodiments of this disclosure relate to touch sensors for display devices, in particular touch sensors for display devices having a double routing wire structure.
Discussion of the Related Art
Touch sensors are installed in display devices such as liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), organic light emitting diode display (OLED) devices, and electrophoresis display devices. The touch sensors are used as a kind of input device capable of inputting predetermined information when a user presses or touches a screen of the display device while watching the display device.
The touch sensors used in the display devices may be classified into an add-on type touch sensor, an on-cell type touch sensor, and an integrated type (or in-cell type) touch sensor depending on their structures. The add-on type touch sensor is configured such that a display device and the add-on type touch sensor are individually manufactured and then the add-on type touch sensor is attached to upper substrates of the display devices. The on-cell type touch sensor is configured such that components constituting the on-cell type touch sensor are directly formed on a surface of an upper glass substrate of the display device. The integrated type touch sensor is configured such that it is mounted inside the display device to thereby achieve thin profile of the display device and to increase durability of the display device.
However, because the add-on type touch sensor has the structure in which it is mounted on the display device, an entire thickness of the display device increases. Further, visibility of the display device is reduced because of a brightness reduction of the display device by the thickness increase. Because the on-cell type touch sensor has the structure in which the on-cell type touch sensor is formed on the surface of the upper glass substrate of the display device, the on-cell type touch sensor shares the upper glass substrate with the display device. Therefore, a thickness of the display device using the on-cell type touch sensor is less than that of the display device using the add-on type touch sensor. However, the entire thickness of the display device using the on-cell type touch sensor also increases because of a touch driving electrode layer, a touch sensing electrode layer, and an insulating layer for insulating the touch driving electrode layer and the touch sensing electrode layer, which constitute the on-cell type touch sensor. Further, the number of processes and the manufacturing cost in the on-cell type touch sensor increase.
The integrated type touch sensor can solve the problems generated in the add-on type touch sensor and the on-cell type touch sensor because of advantages of the thin profile and the durability improvement.
Hereinafter, an example of a related art touch sensor applied to an OLED display device will be described in greater detail with reference to FIGS. 1 and 2. FIG. 1 is a plan view illustrating a related art touch sensor, and FIG. 2 is a cross-sectional view partially illustrating the touch sensor integrated type OLED display device in which a touch sensor is applied to an OLED display device.
Referred to FIGS. 1 and 2, the touch sensor integrated type OLED display device includes an OLED display panel DP, a touch sensor TS and a sealant S for adhering the touch sensor TS to the OLED display panel DP.
The OLED display panel DP includes a lower substrate 10 on which thin film transistors (not shown) are formed. The OLED display panel DP also includes an anode electrode 12, an organic light emitting layer 14, a cathode electrode 16 and an organic layer 18 which are sequentially formed on the lower substrate 10. Also, the OLED display panel DP includes touch pads TP′ formed on the lower substrate 10. The touch pad TP′ is connected with a first pad TP or a second pad RP by a conductor 30. The connection portion 19 is connected with the touch pad TP′, and extended from the touch pad TP′ to the exterior of the sealant S.
The touch sensor TS includes an upper substrate 20, a plurality of first touch electrode serials Tx formed on the upper substrate 20 and arranged in parallel with a first direction (e.g. x direction), and a plurality of second touch electrode serials Rx arranged in a second direction (e.g. y direction) which crosses the first direction and electrically insulated from the plurality of first touch electrode serials Tx. The plurality of first and second touch electrode serials Tx and Rx function as components of the touch sensor. The touch sensor TS includes a plurality of first routing wires RW1 and a plurality of second routing wires RW2. The plurality of first and second routing wires RW1 and RW2 are formed at outside of a region in which the plurality of first and second touch electrode serials Tx and Rx are formed. Also, the plurality of first routing wires RW1 are respectively connected with the plurality of first touch electrode serials Tx, and the plurality of second routing wires RW2 are respectively connected with the plurality of second touch electrode serials Rx. Also, the touch sensor TS includes a plurality of first pads TP and a plurality of second pads RP formed one edge of the upper substrate 20. The plurality of first pads TP are respectively connected with the plurality of first routing wires RW1, and the plurality of second pads RP are respectively connected with the plurality of second routing wires RW2.
Each of the plurality of first touch electrode serial Tx has a plurality of first electrode patterns 22a, and a plurality of first connection patterns 22b which connect neighboring first electrode patterns 22a with each other. Each of the plurality of second touch electrode serial Rx has a plurality of second electrode patterns 24a, and a plurality of second connection pattern 24b which connect neighboring second electrode patterns 24a with each other. The first connection pattern 22b of the first touch electrode serial Tx crosses over the second connection pattern 24b of the second touch electrode serial Rx to be is electrically insulated from each other.
However, in the touch sensor integrated type OLED devises, entire resistance value of the first and second routing wires RW1 and RW2 is large because the touch sensor has a single routing wire structure in which the first routing wire RW1 is connected with only one end of the first touch electrode serial Tx, and the second routing wire RW2 is connected with only one end of the second touch electrode serial Rx.
On the other hand, the related art touch sensor integrated type LCD device also has the same problems as the related art touch sensor integrated type OLED device because it has a structure in which components of the touch sensor are formed on a color filter substrate or a thin film transistor substrate and routing wires has the single routing wire structure.
In general, touch sensibility of the touch sensor depends on time constant of a resistor-capacitor circuit in the touch sensor. Herein, the time constant (τ) of the resistor-capacitor circuit is equal to the product of the circuit resistance R (ohms) and the circuit capacitance C (farads), i.e. τ=R×C. Thus, the smaller the time constant of the resistor-capacitor circuit is, the better sensibility of the touch sensor is because the time constant is proportional to magnitude of the total resistance of the resistor-capacitor circuit. Accordingly, it is necessary to reduce the magnitude of the resistance for enhancing the sensibility of the touch sensor.